The exhaust gas discharged from an internal combustion engine has a high temperature, typically about 850.degree. F. to 1200.degree. F. In some applications the exhaust must be cooled before it is discharged into the atmosphere to reduce the safety hazard of the hot exhaust. Heat recovery mufflers have been used also to recover energy that would otherwise be wasted in the exhaust discharge. The recovered energy can be used directly as heat or it can be converted to mechanical energy to provide a supplement to the main engine drive power. Some heat recovery systems include an exhaust gas muffler that cools the exhaust gas and may provide an auxiliary source of heated water.
In a heat recovery muffler, the main objective is to attenuate the sound energy and remove heat from the exhaust gas, while maintaining the exhaust gas pressure drop within an acceptable limit.
The present exhaust gas recuperator is of the type disclosed in U.S. Pat. No. 4,450,932, issued May 29, 1984, to Mostafa M. Khosropour and Thomas C. Learn, for Heat Recovery Muffler. Typical embodiments of the present invention omit some of the secondary features of the cited muffler (although some of them may be included optionally), and they include other features making them advantageous for certain purposes.
The heat recovery muffler of Khosropour and Learn (K&L) comprises an outer body with an annular heat exchanger disposed therein and spaced from each end. The heat exchanger has a central opening surrounding an exhaust gas inlet pipe to provide an annular passage. The downstream end of the central opening is closed off so that the flow of exhaust gas through the inlet pipe is reversed and is directed back upstream. A plurality of tubes communicate between opposite ends of the body, so that the exhaust gas then flows downstream through the tubes in heat exchange relation with a cooling medium, such as water, to cool the exhaust gas and heat the cooling medium. The cooled exhaust gas is discharged to the atmosphere through an outlet pipe in the downstream end of the body.